Alignment telescope



C. W. KEUFFEL ETAL July 1 5, 1958 ALIGNMENT TELESCOPE 2 Sheets-Sheet 1Original Filed June 20, 1952 CARL W. KEUFFEL CONWAY D. HILLMAN ALLlSTERL. BAKER A A1 RNEY' y 1953 c. w. KEUFFEL ET AL 2,843,013

ALIGNMENT TELESCOPE Original Filed 'June 20, 1952 2 Sheets-Sheet 2 M mil Q -3 E Q Fig 111 2/4 2/6 INVENTORS CARL W. KEUFFEL CONWAY D. HILLMANALLlSTER. L. BAKER B s ATTO EY United States Patent ALIGNMENT TELESCOPECarl W. Keuifel, Bernardsville, Conway D. Hillman, Millburn, andAllister L. Baker, Denville, N. J., assignors to Keuliel & EsserCompany, Hoboken, N. J., a corporation of New Jersey Originalapplication June 20, 1952, Serial No. 294,652,

now Patent No. 2,784,641, dated March 12, 1957. Divided and thisapplication July 16, 1956, Serial No. 598,212

2 Claims. (Cl. 88-32) This invention relates to an optical instrument ofthe telescope class. More particularly it relates to a telescopesuitable for optical alignment work. Instruments of this general typehave recently been used quite extensively in the aircraft industryforlining up the component parts in the assembly of an aircraft. Some ofthese prior art instruments have micrometer means for measuring thevertical and horizontal displacements necessary to line up a particulartarget with the optical line of sight of the instrument. However inthese instruments, the micrometer means have been provided outside thetelescope objective which has made the instruments complicated in thestructure for operating the micrometer means.

The principal object of the present invention is to provide a telescopefor alignment work which includes optical micrometer means within thetelescope for measuring the displacement necessary to line up aparticular target with the optical line of sight of the instrument.

Another object of the present invention is to provide optical micrometermeans for a telescope, which means operates by translation of an opticalelement laterally transversely across the optical line of sight of thetelescope.

Another object of the invention is to provide optical micrometer meansfor a telescope which produces a displacement directly proportional tothe movement of the displacement means.

Another object of the present invention is to provide a telescope whichincludes optical micrometer means and which can focus from infinity to apoint very close to the objective of the instrument.

These and other objects of the invention and the means for theirattainment will be more fully understood by reference to the followingdescription taken in connection with the accompanying drawing in which:

Fig. I is a view in plan of the new optical instrument.

Fig. II is a broken view in enlarged sectional plan taken through thecenter line of Fig. I.

Fig. III is a diagrammatic view showing an optical arrangement foranother embodiment of the invention.

Fig. IV is a diagrammatic view showing an optical arrangement for athird embodiment of the invention.

Fig. V is a diagrammatic view showing an optical arrangement for afourth embodiment of the invention.

.Fig. VI is a diagrammatic view showing an optical arrangementfor afifth embodiment of the invention.

Fig. VII is a diagrammatic view showing an optical arrangement for asixth embodiment of the invention.

Fig. VIII is a diagrammatic view showing an optical arrangement for-aseventh embodiment of the invention.

The optical parts of the first embodiment of the new telescope are shownin Fig. II. They consist of a positive objective lens 2, made up of apositive component 4 of crown glass and a negative component 6 of fiintglass (the usual achromatic doublet combination); a negative lens 8,made up of a negative component 10 of crown glass and a positivecomponent 12 of flint glass (also an achromatic doublet combination); ashifting lens 14, preferably of high index glass, at positive lens 16,made up of a positive component 18 of crown glass and a negativecomponent 20 of flint glass (an achromatic cemented doubletcombination); the positive lens 16 is considered to be the secondobjective lens of the instrument since parallel rays entering the firstobjective lens 2 will also enter the second objective lens 16 asparallel rays, a positive focussing lens 22, made up of a positivecomponent 24 of crown glass and a negative component 26 of flint glass(an achromatic cemented doublet combination); a rcticle 28 which mayhave a curved surface to correct the position of the exit pupil and afour lens erecting eyepiece 30, the individual lenses of which are notshown in Fig. II.

The spacing between the objective 2 and the negative lens 8 is such thatthe second principal focus of the objective 2 will coincide with thefirst principal focus of the negative lens 8. Thus parallel raysentering the objective lens 2 will leave the negative lens 8 as parallelrays. The second principal focus of a lens (whether positive ornegative) is considered to be the pointof convergence or divergenceafter refraction of parallel rays coming from the direction of theobject or target. Conversely, the first principal focus of a positive ornegative lens is the point of convergence or divergence after refractionof parallel rays coming from the opposite direction.

The shifting lens 14 is the equivalent of a Galilean telescope; i. e.its radii of curvature R and R and its thickness t satisfy the formula:

where n is the index of refraction of the lens with regard to air. Theradii of all convex surfaces are considered positive and the radii ofall concave surfaces are considered negative. A glass of high index ofrefraction is preferably chosen for this component in order to keep thethickness low for the amount of displacement which must be accomplishedin shifting the lens. The transverse or lateral shifting of the element14 is understood to be a translational movement in the directionperpendicular to the optical line of sight of the instrument. If d isthe displacement caused by a transverse lateral shift S of the shiftinglens 14, then:

8 R2 In terms of the thickness and refractive index:

RY For a given displacement and any assumed R a higher index of,refraction, n, means that a thinner lens is required. When, as in Fig.II, the shifting lens 14 is internal, the equivalent of the displacementd at the target will be the quantity calculated from the above formulaemultiplied by the magnification of that part of the optical system whichcomes in front of the lens 14, in this case the combination of theobjective lens 2 and the negative lens 8. If m is the magnification ofthis combination and D is the displacement at the target, then, theequations:-

3 crease the magnification of the telescope whereas in the otherposition it will tend to decrease the magnification. However, in thisembodiment, the effect of the shifting lens 14 on the magnification willusually be small.

The positive lens 16 tends to bring the light passing through theshifting lens 14 to focus on the reticle 28. In the embodiment of Fig.II, the positive focussing lens 22 is required to actually bring thelight to a focus. It would also be possible to focus the positive lens16 itself in which case the focussing lens 22 would not be required or anegative focussing lens could be used. However, a positive focussinglens is preferred because it permits the instrument to be focussed downto a very close near distance. In fact with this type of construction itis possible to design a system which can focus right down to the frontsurface of the objective.

The four lens eyepiece within the tube may be of the type commonly usedin surveying instruments or any other suitable eyepiece may be used. Theoverall magnification of the telescope, M, will be given by the formula:

which equals the magnification of the shifting lens, f is the equivalentfocal length of the combination of the positive lens 16 and thefocussing lens 22 and is the equivalent focal length of the eyepiece.

The objective 2 and the negative lens 8 are carried by the tube withinthe main tube 42. The objective 2 fits within the objective mount 44 andis held therein by the threaded ring 46'. The objective mount 44 isthreaded onto one end of the tube 40. This threaded connection may alsobe used for adjusting the spacing between the objective lens 2 and thenegative lens 8. A mounting plate 48 is threaded onto the other end ofthe tube 40. The mount 50 for the negative component 10 of the negativelens 8 is held against the mounting plate 48 by three screws 52.Oversize holes may be provided in the mount 50 for the screws 52 topermit centering of the negative lens 8 with the objective lens 2. Themount 54 for the positive component 12 of the negative lens 8 screwsover the mount 50 as shown. This threaded connection may also be usedfor the adjustment of the spacing between the negative element 10 andthe positive element 12 of the negative lens 8. A locking ring 56 isprovided to maintain this adjustment. Threaded rings 58 and 60 are alsoprovided to hold the components 10 and 12 in their respective mounts 50and 54. A set screw 62 is provided to hold the tube 40 in the main tube42. A spherical surface which is centered with the optical axis may beprovided on the main tube 42 as is known in the art to form part of aball joint mounting for the telescope when in use.

The shifting lens 14 is carried in the transversely sliding mount 64 andheld therein with a threaded ring 6'6. The transversely sliding mount 64is held between the enlarged outer end 68 of the tube 70 and the plate72. Three spacers 74 are provided between the plate 72 and the enlargedend 68 of the tube 70 and spacers 74 and plate 72 are held thereagainstby the screws '76. All of these parts are very accurately made to insurea close fit and smooth sliding action. The transversely sliding mount 64is moved by means of the sliding wedge 78 which slides in a slot in theenlarged outer end of the tube 68 and a slot in the enlarged portion 80of the tube 70. The action of the sliding wedge 78 is counteracted bythe leaf spring 77 attached to the tube.70 by the screws 79. I

A rack 82 is secured to the sliding wedge 78. The rack 82 is engaged bythe pinion S4. The pinion 84 is held in the axle 86 by a set screw 88.The axle 86 fits where m equals in the bearing 90 which is provided witha flange that is secured to the casting 92 by the screws 94. The washer96 is held onto the axle 86 by the screw 98. The knob 100 is clamped tothe washer 96 by means of the ring 102 and the screws 104. The nut 106which is secured by a set screw 108 holds the axle 86 in the bearing 90.A pin 110 passes through the casting 92 and the main tube 42 to preventthe casting 92 from turning or sliding on the tube 42. The head of thepin 110 may act as a stop limiting the turning of the knob 100. A screwor screws 112 may be provided inside the knob 10% to act against the pin110 in limiting the moiton of the knob 100. The enlarged portions 68 and80 of the tube 70 fit accurately within the main tube 42 and the tube 70is prevented from sliding and turning in the tube 42 by the set screw114.

The knob 100 is provided with a graduated drum 116 (Fig. I). Thisgraduated drum 116 cooperates with an index mark on the outer edge ofthe flange of the bearing 90. The index mark is preferably providednearest the eyepiece end of the telescope for the convenience of theobserver. Since the displacement at the target is proportional to thetransverse movement of the shifting lens according to the formula givenabove, the scale on the graduated drum 116 is uniform. The angle 0 indegrees which the drum 100 must be turned in order to compensate adisplacement D at the target is given by the formula:

where p is the pitch diameter of the pinion 84 and on is the wedge angleof the sliding wedge 78. The graduation of the drum 116' is in accordwith this formula.

The same type of construction may be used for moving the shifting lens14 in the vertical direction and these means are operated by the knob118 (Fig. I) which is also provided with a graduated drum not shown forindicating the vertical displacement at the target.

The positive lens 16 is held in the mount 120 by the tube 122 and thethreaded ring 124. The mount 120 fits in the tube 70 andis held thereinby a screw 79.

The positive focussing lens 22 is held in the tube 126 by the threadedring 128. The tube 126 fits inside the tube 70 and is free to slidetherein. A rack 130 is secured to the tube 126. The rack 130 alsoprevents turning of the tube 126 because it is limited by a slot in thetube 70. The rack 130 is operated by the pinion 132 which may be turnedby means of the knob 134 in exactly the same manner as the pinion 84 isturned by means of the knob 100.

The reticle 28 is spun or cemented in the mount 136 which is supportednear the eye end of the tube 70 by four adjusting screws 138. Washers140 may be provided between the heads of the adjusting screws 138 andthe tube 70. Pin holes are provided in the heads of the adjusting screws138 to permit adjustment of the reticle 136 in both the horizontal andvertical directions. The cap 142 screws over the end of the tube 70 tocover the heads of the adjusting screws 138. The eyepiece bearing 144screws into the end of the tube 70. The eyepiece tube 30 carrying thefour eyepiece lenses slides within the eyepiece bearing 144. A screw 146is attached to the side of the tube 30 and fits into a spiral slot inthe eyepiece bearing 144. A sleeve 148 fits over the eyepiece bearing144 to cover the spiral slot and is held in place by a screw 150. Theknurled focussing ring 152 is secured to the tube 30 by set screw 154.The ring 152 turns the tube 30 for focussing the eyepiece on the reticle28 by means of the spiral groove.

The optical system shown in Fig. III is essentially the same as theoptical system shown in Fig. II except that the negative lens 208 isshown as a single component in Fig. III and no special focussing lens isprovided. The second principal focus of the objective lens 202 coincideswith the first principal focus of the negative lens 208 so that parallelrays entering the objective lens 202 will leave the negative lens 208 asparallel rays. The shifting lens 214 may be moved transversely by themeans shown in Fig. II or any other suitable means. The positive lens216 brings the rays to a focus on the reticle 228 and the lens 216 maybe longitudinally adjustable for focussing the telescope on nearobjects. The eyepiece is made up of the four lenses 232, 234, 236 and238, parallel rays entering the objective 202 coming to a focus betweenthe third and fourth eyepiece lenses 236 and 238 and leaving the fourtheyepiece lens 238 as parallel rays.

In the embodiment of Fig. IV, the positive lens 308 is spaced from theobjective 302 so that its first principal focus coincides With thesecond principal focus of the objective 302. 'Parallel rays entering theobjective 302, leave the positive lens 308 as parallel rays. Theshifting lens 314 lies between the positive lens 308 and the positivelens 316. The positive lens 316 focusses the rays on the reticle 328. Inthis case a two lens eyepiece made up of achromatic lenses 332 and 334is used giving an erect image because of the focal plane between theobjective lens 302 and the positive lens 308. The formulae given aboveapply to this embodiment, if m; is taken as the magnification of thecombination of the objective lens 302 and the positive lens 308. It ispossible to make the optical system of Figs. II or III shorter than theoptical system of Fig. IV and Figs. II and III may be preferred for thisreason.

The shifting lens has utility other than in the type of telescopeillustrated in Fig. II. Fig. V shows a shifting lens 414 which is also aGalilean telescope used in front of the objective 402 of a simpleerecting telescope. The objective 402 forms an image of a target on thereticle 428 which is viewed through the four lens erecting eyepiece madeup of the lenses 432, 434, 436 and 438. In this embodiment, thedisplacement caused by the shifting lens is given directly by theformula:

In Fig. VI, the Galilean telescope shifting element 514 is made up of apositive lens 513 and a negative lens 515. The optical separation L ofthese two lenses is given by the formula:

f being the equivalent focal length of the first lens and f being theequivalent focal length of the second lens. The shifting lens in theother embodiments may also be considered a Galilean telescope, the firstsurface having an equivalent focal length,

the second surface having an equivalent focal length,

and the optical separation L being related to the thickness of the lensby the formula, L=t/ n. In all other respects, the embodiment of Fig. VIis the same as the emwhich would be obtained from the type indicated aselements 14, 214, 314, 414 and 514 in Figs. II-VI. For example, atelescope such as that made up by the positive lens 202 and the negativelens 208 in Fig. III or such as the telescope made up by the twopositive lenses 302 and 308 in Fig. IV may be shifted laterallyaccording to this invention. The shifting lenses 214 and 314 would thenbecome unnecessary in Figs. III and IV and could be omitted.

The embodiment of Fig. VII is the same as the embodiment of Figs. IIIand VI except that a plano parallel tilting plate is used instead of atransversely shifting Galilean telescope. The plano parallel tiltingplate is known in the art but until now its use has been limited to aposition in front of the objective. The element 614 has flat planoparallel surfaces and operates by tilting about an axis whereas theGalilean telescopes 214 and 514 in Figs. III and VI operate by atransverse or lateral translational motion. The displacement caused by apiano parallel tilting plate is given by the formula:

the angle of tilt and r is the angle of refraction corresponding to theangle i; i. e.:

sin sm r= It is evident that in this embodiment, the displacement is notproportional to the angle of tilt so a non-uniform scale must be used orsome other special means such as a cam provided to compensate the nonproportional action.

The embodiment of Fig. VIII is the same as the embodiment of Fig. IIIexcept that illumination means are provided so that the telescope may beused as an autocollimator. For example, the illumination means may takethe form of a lamp 740 and a partial reflector 742 (which may be merelya glass plate) for directing light through the reticle 728. Thus animage of the reticle 728 may be projected out through the objective 702to suitable reflecting means which direct the light back to theobjective 702 and through the rest of the optical system so that animage of the reticle is formed on the reticle. When the reticle is incoincidence with its image, the line of sight of the telescope isperpendicular to the reflecting means. In this manner, the instrumentmay be used for angular alignment as well as for transverse displacementalignment. The embodiments shown in the other figures may of course alsobe used for angular alignment if used in combination with a collimator.

Having thus described the invention, what is claimed l. A telescopecomprising an objective lens, a second lens within the telescope spacedfrom said objective lens at a distance so that its first principal focuswill coincide with the second principal focus of the objective lens, athird lens within the telescope spaced further from said objective lensthan said second lens, a reticle at a focal plane spaced further fromsaid objective lens than said third lens, an eyepiece focussed on saidreticle, a pair of lens elements adjacent one of said lenses havingcoincident principal foci but on the side thereof opposite the focuswhich coincides with the focus of the other lens, one of said lenselements having an equivalent focal length, f the other of said lenselements having an equivalent focal length, f the optical separationbetween said lens elements being L, said quantities satisfying therelation f +f =L, in which the focal length is inserted as a negativequantity for a negative lens, means for moving said pair of lenselements togther laterally to vary the displacement of the image of agiven target, the displacement of the image of a given target, thedisplacement of the image being proportional to the lateral movement ofsaid pair of lens elements and means for measuring the lateral movementof said pair of elements to make said reticle appear in alignment withthe given target.

2. A telescope comprising an objective lens, a reticle at a focal planeof the telescope, an eyepiece focused on said reticle, a pair of lenselements in front of said objective lens, one of said lens elementshaving an equivalent focal length f the other of said lens elementshavlens to make said reticle appear in alignment with the ing anequivalent focal length f the optical separation given target.

between said lens elements being L, said quantities satisfying thegelation f1+f2= in Whichf the focal g i f2 References Cited in the fileof this patent is inserte as a negative quantity or a negative ens, 5

means for moving said pair of lens elements together UNITED STATESPATENTS laterally to vary the displacement of the image of a given2,784,641 Keuffel et a1 Mar. 12, 1957 target, the displacement of theimage being proportional to the lateral movement of said pair of lenselements and FOREIGN PATENTS means for measuring the lateral movement ofsaid second 10 552,355 France J an. 19, 1923

